The problem is the mime type (how an application determines which file to open with which application) is not registered.
One option is to copy the magnet link, open your torrent client and use option "open magnet URI" and paste the magnet URI there.
Second option, download .torrent file or create a plain text document with extension .torrent and paste the magnet link in it. Open the downloaded or created torrent file in your torrent client.
Third and most convenient solution, set up your browser so that it can open magnet link.
Here is guide for firefox browser - How can I get Firefox to open torrent files with Transmission?. You have to adjust the steps if configuring for any other client like vuze.
Most important thing to remember, most application get installed in
/usr/bin, so you need to search the torrent client there.